sysfb: Fix screen_info type check for VGA

Use the helper screen_info_video_type() to get the framebuffer
type from struct screen_info. Handle supported values in sorted
switch statement.

Reading orig_video_isVGA is unreliable. On most systems it is a
VIDEO_TYPE_ constant. On some systems with VGA it is simply set
to 1 to signal the presence of a VGA output. See vga_probe() for
an example. Retrieving the screen_info type with the helper
screen_info_video_type() detects these cases and returns the
appropriate VIDEO_TYPE_ constant. For VGA, sysfb creates a device
named "vga-framebuffer".

The sysfb code has been taken from vga16fb, where it likely didn't
work correctly either. With this bugfix applied, vga16fb loads for
compatible vga-framebuffer devices.

Fixes: 0db5b61e0dc0 ("fbdev/vga16fb: Create EGA/VGA devices in sysfb code")
Cc: Thomas Zimmermann <[email protected]>
Cc: Javier Martinez Canillas <[email protected]>
Cc: Alex Deucher <[email protected]>
Cc: Tzung-Bi Shih <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: "Uwe Kleine-König" <[email protected]>
Cc: Zsolt Kajtar <[email protected]>
Cc: <[email protected]> # v6.1+
Signed-off-by: Thomas Zimmermann <[email protected]>
Reviewed-by: Tzung-Bi Shih <[email protected]>
Reviewed-by: Javier Martinez Canillas <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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